Overview of the Innate vs. Adaptive Immune System

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Immunology

Summary

The immune system is divided into two branches -- innate and adaptive immune systems. The innate immune system, is evolutionarily older and is always active within the body. It responds quickly to any pathogen, but is non-specific. This system operates with cells that detect common patterns on pathogens and injured cells. Functions of the innate immune system include forming physical barriers, recruiting leukocytes (white blood cells) to sites of injury or infection, and providing antiviral defenses. The key players in the innate immune system are neutrophils, macrophages, dendritic cells, mast cells, natural killer cells and the complement system. But don't forget, the epithelium also plays a critical role! In contrast, the adaptive immune system is slower to react but excels in specificity. The adaptive immune system distinguishes specific antigens, allowing it to respond to a wide range of very specific antigens. It also has the ability to differentiate between the body's cells and external harmful agents. One of its most significant features is immunological memory, whereby the immune response improves with each exposure to a specific antigen. The adaptive immune system is further divided into humoral immunity and cell-mediated immunity. Humoral immunity targets extracellular pathogens and utilizes B-cells to generate antibodies that neutralize foreign antigens. Cell-mediated immunity, on the other hand, targets intracellular pathogens, primarily enlisting T-cells, including cytotoxic T-cells and helper T-cells, to destroy microbes within phagocytes.

Lesson Outline

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FAQs

What is the role of the thymus in T-lymphocyte maturation?

The thymus plays a critical role in T-cell maturation as it is the primary site where thymocytes (immature T-cells) mature into functional T cells. In the thymus, thymocytes undergo a series of developmental stages characterized by various processes such as VDJ recombination, which ultimately results in a diverse repertoire of T-cell receptors (TCRs). These TCRs allow T-cells to recognize a variety of antigens, making them key players in the adaptive immune response.

Can you explain the difference between CD4+ and CD8+ T-cells?

CD4+ and CD8+ T-cells play different roles in the immune response. CD4+ T-cells, also known as helper T-cells, coordinate the immune response by stimulating other immune cells, including B-cells, to fight off infections. On the other hand, CD8+ T-cells, also known as cytotoxic T-cells, directly kill infected cells. These cells recognize different classes of antigens and their differentiation depends on signals received during thymic selection processes.

What is meant by positive and negative selection in the maturation of T-lymphocytes?

Positive and negative selection are crucial processes in T-cell maturation that occur in the thymus and lead to central tolerance. Positive selection ensures that T-cells have T-cell receptors (TCRs) that can interact with MHC molecules, a crucial element for antigen presentation. T-cells that do not pass this selection process undergo apoptosis. Conversely, negative selection eliminates T-cells with high affinity for self-antigens, preventing autoimmune responses. T-cells that bind too strongly to self-antigens are induced to undergo apoptosis, ensuring that these cells do not harm the body's own tissues.

How is VDJ recombination significant in T-cell maturation?

VDJ recombination is a mechanism of somatic recombination that enables the enormous diversity of the T-cell receptor (TCR). It helps in generating a large repertoire of T-cells, each capable of recognizing a different antigen. Diversity in the immune system is vital as it allows the immune system to respond to a wide array of pathogens and other foreign substances. VDJ recombination occurs during T-cell maturation in the thymus and contributes to both the diversity and specificity of the immune response.

How does the failure of negative selection contribute to autoimmune diseases?

Negative selection is key in promoting central tolerance, the immune system's ability to avoid attacking its own tissues. When this process fails, T-cells with a high affinity for self-antigens are not removed and can circulate in the body. These cells may then target the body's own cells for destruction, leading to autoimmune diseases. Thus, successful negative selection is essential for preventing autoimmunity.

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